web容器在啟動的時候，它會為每一個web程式建立一個對應的ServletContext物件，它代表了當前的web應用；

1、共享資料

我在這個Servlet中儲存的資料，可以在另外一個servlet中拿到；

 1 package com.kuang.servlet;
 2 
 3 import javax.servlet.ServletContext;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 
 7 import javax.servlet.http.HttpServletResponse;
 8 import java.io.IOException;
 9 
10 public class HelloServlet extends HttpServlet {
11     @Override
12     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
13 
14         //this.getInitParameter()     初始化引數
 
15         //this.getServletConfig()     Servlet配置
16         //this.getServletContext()    Servlet上下文
17         ServletContext context = this.getServletContext();
18 
19         String username = "王劉"; //資料
20         context.setAttribute("username",username); //將一個數據儲存在了ServletContext中，名字為：username，值username
 

21 
22 
23     }
24 
25     @Override
26     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
27         doGet(req, resp);
28     }
29 }

獲取資料：

 1 package com.kuang.servlet;
 2 
 3 import javax.servlet.ServletContext;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import java.io.IOException;
 9 
10 public class GetServlet extends HttpServlet {
11     @Override
12     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
13         ServletContext context = this.getServletContext();
14         String username = (String) context.getAttribute("username");
15 
16         resp.setContentType("text/html");
17         resp.setCharacterEncoding("utf-8");
18         resp.getWriter().print("名字："+username);
19     }
20 
21     @Override
22     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
23         doGet(req, resp);
24     }
25 }

註冊：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
 3          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
 5                       http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
 6          version="4.0"
 7          metadata-complete="true">
 8 
 9     <servlet>
10         <servlet-name>hello</servlet-name>
11         <servlet-class>com.kuang.servlet.HelloServlet</servlet-class>
12     </servlet>
13     <servlet-mapping>
14         <servlet-name>hello</servlet-name>
15         <url-pattern>/hello</url-pattern>
16     </servlet-mapping>
17 
18     <servlet>
19         <servlet-name>getc</servlet-name>
20         <servlet-class>com.kuang.servlet.GetServlet</servlet-class>
21     </servlet>
22     <servlet-mapping>
23         <servlet-name>getc</servlet-name>
24         <url-pattern>/getc</url-pattern>
25     </servlet-mapping>
26 
27 
28 </web-app>